Just months after the "Horsemeat" scandal, an investigation for the BBC today revealed tests which showed there was a less than 1 per cent chance that a pack of chops labelled as British came from the British Isles.

Tesco today said it was "extremely disappointed" by the discovery and had told its supplier that "this mistake is unacceptable".

The supermarket giant sources its pork from Cranswick Country Goods, which in turn bought the meat from F A Gill, a family-owned company in Wolverhampton.

FA Gill said it was just one of a number of suppliers to Cranswick, adding: "F A Gill can categorically deny that the pork came from their supply as they do not deal with Dutch meat."

Cranswick insisted that subsequent tests had not revealed similar problems. The investigation for Radio 4's You & Yours and Farming Today programme followed earlier tests on the authenticity of 40 other samples taken from across the industry.

The meat was tested at a lab in Germany, where scientists used 'Stable Isotope Ratio Analysis', a technique that compares meat to a database of samples taken from kery parts of the country.

Tesco's meat bore the Red Tractor logo, designed to show a product can be traced back to a British farm. The supermarket has made a huge effort to reassure customers about the quality and provenance of its meat ever since the Horsemeat scandal broke earlier this year.

Tesco was one of the first to be highlight by food safety officials as having sold burgers containing horsemeat, though fierce rival Asda had more affected products. In February, Tesco vowed to buy 100 per cent British chicken as part of its fightback and sell more meat from "closer to home".

Mick Sloyan from the British Pig Executive today said: "Human error can occur. This is not going to happen on a regular basis. I think we have show that this technology works and it provides an extra level of reassurance for consumers in the traceability systems that we adopt."

In a statement Tesco said the test was just one result on one packet of chops. A spokeswoman said: "We are extremely disappointed to discover a pork loin product probably came from a Dutch farm, not a British farm. When we specify that we want British pork, we expect to be supplied with British pork."

Tesco added: "We have spoken with our supplier to make clear that this mistake is unacceptable."